The bw 58mm dark red 092 infrared filter which looks dark purplish red when held in front of a light source blocks visible light up to 650 nm and passes only 50 of the radiation just below 700 nm thus the dark red colour from 730 nm to 2000 nm transmission is greater than 90 this makes photographs of pure red and infrared images possible with the best utilisation of the relatively low sensitivity of infrared films as the sensitisation of infrared black and white films barely extends